U.S. patent application number 15/479681 was filed with the patent office on 2018-10-11 for radiation shield for near-infrared detectors.
The applicant listed for this patent is Kaiser Optical Systems Inc.. Invention is credited to Alfred Feitisch, Joseph B. Slater, James M. Tedesco.
Application Number | 20180292266 15/479681 |
Document ID | / |
Family ID | 61906726 |
Filed Date | 2018-10-11 |
United States Patent
Application |
20180292266 |
Kind Code |
A1 |
Slater; Joseph B. ; et
al. |
October 11, 2018 |
RADIATION SHIELD FOR NEAR-INFRARED DETECTORS
Abstract
A radiation shield for near-infrared detectors of the type used
in Raman spectroscopic systems comprises a chamber enclosing the
detector and a cooling device in thermal contact with the chamber
and the detector to reduce the level of unwanted radiation to which
the detector would otherwise be exposed. The chamber may include a
window in optical alignment with the detector, and the window may
include one or more coatings to pass wavelengths in a range of
interest or block radiation at wavelengths outside of this range.
The shield may be enclosed in an evacuated dewar having a window
which may also include one or more coatings to favor the wavelength
range.
Inventors: |
Slater; Joseph B.; (Dexter,
MI) ; Tedesco; James M.; (Livonia, MI) ;
Feitisch; Alfred; (Rancho Cucamonga, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaiser Optical Systems Inc. |
Ann Arbor |
MI |
US |
|
|
Family ID: |
61906726 |
Appl. No.: |
15/479681 |
Filed: |
April 5, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J 5/061 20130101;
G01J 2005/065 20130101; G01J 3/4406 20130101; G01J 3/44 20130101;
G01J 5/046 20130101; G01N 21/65 20130101 |
International
Class: |
G01J 5/06 20060101
G01J005/06; G01N 21/65 20060101 G01N021/65; G01J 3/44 20060101
G01J003/44 |
Claims
1. A radiation shield for a near-infrared detector, comprising: a
chamber including an aperture and a near-infrared detector having
at least one detector element, the chamber composed of a thermally
conductive material, the detector disposed within the chamber and
opposite the aperture; and a cooling device in thermal contact with
the chamber and structured to lower the temperature of the chamber
to reduce the emission from the chamber of unwanted radiation
incident upon the detector, wherein the aperture is sized relative
to a distance from the detector to an optic of a spectrograph such
that only a desired solid angle is incident upon the detector,
enabling the detector to receive electromagnetic signals in a
desired spatial range from the spectrograph and attenuating
non-signal bearing electromagnetic radiation from incidence upon
the detector.
2. The radiation shield of claim 1, wherein in the desired
operational wavelength range is 0.4 to 2.5 microns, and the
electromagnetic signals are Raman signals.
3. The radiation shield of claim 1, the radiation shield further
comprising a window covering the aperture in the chamber, wherein
the window is composed of glass, glass-ceramic, diamond,
crystalline quartz, silicon, germanium, gallium nitride crystals,
aluminum nitride crystals, optical metamaterial, transparent
ceramic or a combination thereof.
4. The radiation shield of claim 1, the radiation shield further
comprising a window covering the aperture in the chamber, wherein
the window includes one or more coatings capable of selectively
passing the desired operational wavelength range and/or blocking
radiation at wavelengths outside the desired operational wavelength
range.
5. The radiation shield of claim 1, wherein the chamber is disposed
within an evacuated dewar including a dewar window optically
aligned with the aperture and the detector, wherein the dewar
window includes one or more coatings capable of selectively passing
the desired operational wavelength range and/or blocking radiation
at wavelengths outside the desired operational wavelength
range.
6. The radiation shield of claim 1, wherein the chamber is composed
of metal, metal alloy, non-metal, ceramic, glass, mono-crystalline
material, poly-crystalline material and/or composite material.
7. The radiation shield of claim 6, wherein the chamber material
has a thermal conductivity greater than 30 Watts per
meter-Kelvin.
8. The radiation shield of claim 6, wherein the chamber material
has a thermal conductivity greater than 100 Watts per
meter-Kelvin.
9. The radiation shield of claim 1, wherein the chamber is composed
of an allotrope of carbon, the chamber includes a wall having a
thickness that transitions from a monocrystalline or
polycrystalline allotrope of carbon at an exterior surface of the
wall to an array of columns or spires at an interior surface of the
wall, wherein the columns or spires are proportioned and
distributed to maximize absorption of radiation in the operational
wavelength range of the detector.
10. The radiation shield of claim 1, wherein the chamber has an
interior surface with an emissivity less than 0.1, 0.3 or 0.5 in
the infrared range.
11. The radiation shield of claim 10, wherein the interior surface
includes a surface treatment.
12. The radiation shield of claim 1, wherein the chamber has an
interior surface with a surface treatment having an absorptivity
greater than 0.5, 0.7 or 0.9 in the operational wavelength
range.
13. The radiation shield of claim 1, wherein the chamber has an
exterior surface with an emissivity less than 0.2 and/or a
reflectivity greater than 0.8 in the infrared range.
14. The radiation shield of claim 13, wherein the exterior surface
includes a surface treatment.
15. The radiation shield of claim 1, wherein the detector is an
Indium-Gallium-Arsenide, Indium-Arsenide, Silicon, Germanium,
Silicon-Germanium, Lead-Sulfide, Lead-Selenide or
Mercury-Cadmium-Telluride detector.
16. The radiation shield of claim 1, wherein the detector is a
multi-element detector.
17. The radiation shield of claim 1, wherein the cooling device is
a solid-state cooler, a cyclic compression-expansion cooler or a
cryogenic cooler.
18. The radiation shield of claim 1, wherein the chamber includes
an opening in a wall adjacent the cooling device and the cooling
device is a multi-stage cooling device including a first stage in
thermal contact with the chamber and operative to cool the chamber
to an intermediate temperature, and a second stage in thermal
contact with the detector and operative to cool the detector to a
target temperature lower than the intermediate temperature.
19. The radiation shield of claim 1, wherein the chamber includes
an opening in a wall adjacent the cooling device and the cooling
device is a multi-stage cooling device including a first stage in
thermal contact with the detector and operative to cool the
detector to an intermediate temperature, and a second stage in
thermal contact with the chamber and operative to cool the chamber
to a target temperature lower than the intermediate
temperature.
20. A Raman spectroscopic system, comprising: a spectrograph
configured to generate Raman spectra in a desired wavelength range,
the spectrograph including an optic adapted to transmit the spectra
only within a desired solid angle, the desired solid angle
including a desired signal; a near-infrared detector configured to
receive the desired signal and output electrical signals
representative of the spectra with a desired operational wavelength
and spatial range, wherein the detector is disposed in a radiation
shield, the shield including a chamber composed of a thermally
conductive material and including an opening in opposing relation
to the detector, wherein the opening is sized relative to a
distance from the detector to the optic of the spectrograph such
that only the desired solid angle containing the desired signal is
incident upon the detector, enabling the detector to receive the
Raman spectra from the spectrograph through the opening; and a
cooling device in contact with the chamber to lower the temperature
of the chamber to reduce the emission of unwanted radiation from
the chamber to which the detector would otherwise be exposed.
21. The system of claim 20, the system further comprising a window
covering the opening in the chamber, wherein the window is
constructed of glass, glass-ceramic, diamond or transparent
ceramic.
22. The system of claim 21, wherein the window includes one or more
coatings to pass the desired operational wavelength range of
interest or block radiation at wavelengths outside the desired
operational wavelength range of interest.
23. The system of claim 20, wherein the chamber is disposed within
an evacuated dewar including a dewar window in optical alignment
with the opening into the chamber.
24. The system of claim 23, wherein the dewar window includes one
or more coatings to pass the desired operational wavelength range
or block radiation at wavelengths outside the desired operational
wavelength range.
25. The system of claim 20, wherein the chamber is composed of
metal, metal alloy, non-metal, ceramic, glass, mono-crystalline
material, poly-crystalline material and/or composite material.
26. The system of claim 20, wherein the chamber material has a
thermal conductivity greater than 100 Watts per meter-Kelvin.
27. The system of claim 20, wherein the chamber has an interior
surface with an emissivity less than 0.1, 0.3 or 0.5 and an
exterior surface with a reflectivity greater than 0.5, 0.7 or
0.9.
28. The system of claim 20, wherein the cooling device is a
multi-stage device including a first stage in thermal contact with
the chamber and operative to cool the chamber to an intermediate
temperature, and a second stage in thermal contact with the
detector and operative to cool the detector to a target temperature
lower than the intermediate temperature.
29. The system of claim 20, wherein the cooling device is a
multi-stage device including a first stage in thermal contact with
the detector and operative to cool the detector to an intermediate
temperature, and a second stage in thermal contact with the chamber
and operative to cool the chamber to a target temperature lower
than the intermediate temperature.
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to spectroscopy
and, in particular, to a radiation shield for detectors operating
in the near-infrared.
BACKGROUND
[0002] Certain Raman systems operate with pump wavelengths in the
near-infrared (NIR) range (typically wavelengths of 0.7 to 2.5
microns). Such systems have an advantage in certain application
spaces in that they reduce the amount of fluorescence signal
contamination. A disadvantage, however, is that this wavelength
range contains significant and detectable amounts of blackbody
radiation which manifests itself as background noise, which can
reduce the sensitivity, specificity and accuracy of the Raman
measurement. This background is generated from the "scene,"
including the surfaces of the instrumentation facing the detector.
Typically such surfaces include the inside walls of the detector
housing, the window of the detector housing, and any spectrograph
surface and components in line of sight to the detector
surface.
[0003] In typical Raman spectroscopy applications, such as
astronomy, industrial process control, pharmaceutical and or
bio-pharma composition, process and quality control and the like,
the detector can be cooled to well below ambient temperatures,
typically using a thermoelectric (TE) stack. While this minimizes
dark noise generated within the detector itself, it does not solve
problems associated with the undesirable radiation incident upon
the detector. Accordingly, there remains a need for further
contributions in this area of technology.
SUMMARY
[0004] According to at least one aspect of the present disclosure,
a radiation shield for a near-infrared (NIR) detector includes: a
chamber including an NIR detector and an aperture, the chamber
composed of a thermally conductive material, the detector disposed
within the chamber and opposite the aperture, and the shield
further including a cooling device in thermal contact with the
chamber and structured to lower the temperature of the chamber to
reduce the emission from the chamber of unwanted radiation incident
upon the detector, wherein the aperture is configured to enable the
detector to receive electromagnetic signals in a desired
operational wavelength range of interest from a spectrograph. The
desired operational wavelength range may be 0.4 to 2.5 microns, and
the electromagnetic signals are Raman signals. In certain
embodiments, the radiation shield further comprises a window
covering the aperture in the chamber. In further embodiments, the
window includes one or more coatings capable of selectively passing
the operational wavelength range and/or blocking radiation at
wavelengths outside the operational wavelength range.
[0005] In at least one embodiment, the chamber is disposed within
an evacuated dewar including a dewar window optically aligned with
the aperture and the detector, wherein the dewar window includes
one or more coatings capable of selectively passing the operational
wavelength range and/or blocking radiation at wavelengths outside
the operational wavelength range. In certain embodiments, the
chamber has an inside surface with a relatively low emissivity in
the infrared range. In further embodiments, the chamber has an
outside surface with a relatively high reflectivity in the infrared
range.
[0006] According to another aspect of the present disclosure, a
Raman spectroscopic system includes: a spectrograph outputting
Raman spectra in a near-infrared (NIR) optical range; a detector
configured to receive the spectra and output electrical signals
representative of the spectra with an operational wavelength range,
wherein the detector is disposed in a radiation shield, the shield
including a chamber composed of a thermally conductive material and
including an opening in opposing relation to the detector enabling
the detector to receive the Raman spectra from the spectrograph
through the opening; and a cooling device in contact with the
chamber to lower the temperature of the chamber and reduce the
level of unwanted radiation to which the detector would otherwise
be exposed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The described embodiments and other features, advantages and
disclosures contained herein, and the manner of attaining them,
will become apparent and the present disclosure will be better
understood by reference to the following description of various
embodiments of the present disclosure taken in junction with the
accompanying drawings, wherein:
[0008] FIG. 1 shows a cross-sectional view of an exemplary
embodiment according to the present disclosure, including a
thermoelectric cooling device;
[0009] FIG. 2 shows a cross-sectional view of further embodiment
according to the present disclosure, including a multi-stage
thermoelectric cooling device;
[0010] FIG. 3 shows a cross-sectional view of an alternative
embodiment according to the present disclosure; and
[0011] FIG. 4 shows a cross-sectional view of a further embodiment
according to the present disclosure.
DETAILED DESCRIPTION
[0012] The present application discloses various embodiments of a
radiation shield for near-infrared (NIR) detectors. Embodiments
according to the present disclosure reduce the exposure of NIR
detectors to unwanted radiation by surrounding the detector with
the disclosed radiation shields. According to one aspect of the
present disclosure, the shield includes a chamber enclosing the
detector, which is disposed opposite an opening in the chamber
enabling the detector to receive Raman signals in a desired NIR
wavelength range from a spectrograph. According to a further aspect
of the present disclosure, the chamber may include a cooling
device, such as a thermoelectric stack and/or a cyclic
compression-expansion cooler, to lower the temperature of the
chamber to reduce the level of background noise generated in the
detector. Ideally, all surfaces to which the detector is exposed
would have as low a temperature as possible, with the desired
emissivity properties, to minimize the amount of unwanted radiation
getting to the detector. For the purposes of promoting an
understanding of the principles of the present disclosure,
reference will now be made to the embodiments illustrated in the
drawings, and specific language will be used to describe the same.
It will nevertheless be understood that no limitation of the scope
of this disclosure is thereby intended. In particular, though the
present disclosure is described with respect to Raman spectroscopic
systems, the disclosed radiation shields may be applied to
detectors other than NIR detectors used in Raman spectroscopic
systems.
[0013] FIG. 1 illustrates a radiation shield 100 according to an
embodiment of the present disclosure. As shown in FIG. 1, the
shield 100 includes a chamber 112 defining a shield volume 115 and
having an aperture 113. In certain embodiments, the shield 100 may
be disposed within a vacuum-sealed case or dewar 104, which
receives electromagnetic spectra 108 from a spectrometer 102. In at
least one embodiment, the electromagnetic spectra 108 may be Raman
spectra from a Raman spectrometer. The dewar 104 includes a dewar
window 106 which is sealed to the environment to define an
evacuated volume 105, in which the shield 100 is disposed.
[0014] The shield 100 may include a detector 110 disposed within
the shield volume 115 opposite the aperture 113 such that the
electromagnetic spectra 108 transmitted through the dewar window
106 and the aperture 113 falls incident upon the detector 110, as
shown in FIG. 1. The aperture 113 is sized relative to its distance
from detector 110 to enable only those steradians necessary to
transmit the desired spectra 108 to see the detector 110, and the
chamber 112 is proportioned to cover or block all the steradians
not necessary to transmit the desired spectra 108.
[0015] The detector 110 may be any type of detector suitable for
the desired application of the shield 100. For example, the
detector 110 may be at least one of an InGaAs
(Indium-Gallium-Arsenide), InAs (Indium-Arsenide), Si (Silicon), Ge
(Germanium), SiGe (Silicon-Germanium), PbS (Lead-Sulfide), Pb Se
(Lead-Selenide), or MCT (Mercury-Cadmium-Telluride) detector and
the like. The detector 110 may be configured as an array having at
least one detecting element, specifically, the detector 110 maybe
structured as a single element or a multi-element detector. In a
single element embodiment, for example, a Raman spectrum may be
scanned over a single element detector, particularly for a narrow
band for an analyte-specific application.
[0016] The at least one detector element can be one of a CCD
(charge coupled device), a CMOS (complementary metal oxide
semiconductor), a photodiode with a p-n junction, a PIN photodiode
with an intrinsic semiconductor material between the p and n
semiconductors and the like. In at least one application of the
present disclosure, the detector 110 may be a line or 2D array type
InGaAs detector, such as a 1024 pixel linear InGaAs photodiode
array as manufactured by Sensors Unlimited (Part No. SU1024LE-1.7).
The detector 110 may have a desired operational wavelength range
that at least includes the range of the electromagnetic spectra 108
and the spectrometer 102. In certain embodiments, the desired
operational wavelength range of the detector 110 may be around 0.4
to 2.5 microns. In alternative embodiments, the desired operational
wavelength range of the detector 110 may be approximately 0.9 to
1.4 microns or approximately 1.0 to 1.31 microns.
[0017] In at least one embodiment, the chamber 112 is thermally
conductive and, accordingly, is made of a material having a
relatively high thermal conductivity--for instance, greater than
100 Watts per meter-Kelvin (W/mK). In certain embodiments, the
chamber 112 is made of a material having a thermal conductivity
greater than about 250 W/mK. The chamber 112 may be at least
partially composed of a thermally conductive metal, metal alloy,
non-metal, ceramic, glass, mono-crystalline material,
poly-crystalline material and/or composite material. For example,
the chamber may include a metal, such as copper or aluminum, or a
metal alloy, such as oxygen-free high thermal conductivity (OFHC)
copper, copper-tungsten (CuW) or other suitably thermally
conductive metal or alloy. The chamber 112 may include a thermally
conductive ceramic such as beryllium oxide (BeO), aluminum nitride
(AlN), silicon nitride (Si.sub.3N.sub.4), carbides such as silicon
carbide (SiC), complex borides or other suitable ceramic. In
further embodiments, the chamber 112 may include a thermally
conductive composite material such as a diamond/metal composite.
Exemplary suitable metal/diamond composites include copper/diamond,
aluminum/diamond, silver/diamond and diamond/copper-titanium. In
such embodiments, the diamond/metal composites may be fabricated by
a sintering process to improve wettability between the diamond and
the metal matrix. In certain embodiments, the chamber 112 may be a
material having a thermal conductivity as low as 10 W/mK, 20 W/mK
or 30 W/mK. Exemplary materials in this range of thermal
conductivities include nickel-iron alloy (i.e., Invar),
nickel-cobalt ferrous alloy (i.e., Kovar) and lead. In further
embodiments, the material of the chamber 112 may have a thermal
conductivity of 40, 50, 60, 70, 80, 90 or 100 W/mK.
[0018] In at least one embodiment, the chamber 112 may be composed
at least partially of an allotrope of carbon, such as diamond. In
such an embodiment, at least a wall of the chamber 112 having a
thickness may be structured to attenuate or prevent re-reflection
of the Raman spectra within the chamber 112 and/or absorption of
thermal radiation from outside the chamber 112. For example, the
wall of the chamber 112 may transition along its thickness from a
monocrystalline or polycrystalline diamond at an exterior surface
of the wall to an array of columns or spires at an interior surface
of the wall, where the columns or spires are proportioned and
distributed to increase absorption and reduce reflectivity of
radiation through the infrared range. Alternatively, the chamber
112 may include nanotubes of carbon at the interior surface whose
proportions and distribution maximize absorption of radiation in
the infrared range. In such embodiments, the surface structure of
the chamber 112 may include features of less than a wavelength in a
predetermined infrared range.
[0019] Generally, the infrared range includes near-infrared (NIR),
mid-infrared and far-infrared wavelengths of approximately 0.7 to
1000 microns collectively. Thermal radiation for objects at
temperatures above approximately -60.degree. C. (i.e., the
temperature of a cooled InGaAs detector array) peaks in the
wavelength range of approximately 13 microns and below. The
aggregate radiation impinging on a detector at wavelengths within
its sensitivity range may affect its performance. Higher
temperature surfaces emit correspondingly higher absolute spectral
radiation in all wavelength ranges, even though the peak radiation
wavelength shifts to shorter wavelengths with increasing
temperature. Accordingly, it may be desirable to reduce both the
temperature and emissivity of surfaces in view of a detector to
reduce thermal background noise.
[0020] In at least one embodiment according to the present
disclosure, the chamber 112 may include a material having a
relatively low emission coefficient (i.e., low emissivity) in at
least the infrared range. In operation, the chamber 112 may have a
temperature between that of the detector 110 and the surrounding
hardware, including the spectrometer 102, from which the chamber
112 partially shields the detector 110. At a certain temperature,
thermal radiation emitted or reflected from the chamber 112 is
sufficiently low so as to not significantly elevate the inherent
detector dark current generated by the cooler detector 110. In such
an embodiment, at least the interior surface of the chamber 112 may
have a low emissivity to limit the cooling of the chamber 112
necessary to reach a condition at which the contribution of the
chamber 112 to the background radiation incident upon the detector
110 is negligible. In such an embodiment, at least the interior
surface of the chamber 112 may be a material having an emissivity
less than about 0.30.The chamber 112 may further include a material
having a relatively high spectral reflectivity, which may be
associated with a low emissivity to reduce the absorption of
external radiation by the chamber 112. Further, the interior
surfaces of the chamber 112 may be a material having a relatively
high absorptivity in the operational NIR range to reduce internal
reflections that may fall incident upon the detector 110. In
certain embodiments, at least the exterior surface of the chamber
112 may have a relatively high spectral reflectivity in the
infrared range to attenuate the absorption of external
radiation.
[0021] In at least one embodiment, the chamber 112 may include
multiple layers or a composite of multiple materials described
herein to attenuate absorption of external radiation, reduce
emission from the interior surface of the chamber 112, and
facilitate thermal conduction from the chamber 112. In all
embodiments, relatively high absorptivity may include
absorptivities greater than 0.5, 0.7 or 0.9; relatively high
spectral reflectivity may include reflectivities greater than 0.5,
0.7 or 0.9; and relatively low emissivity may include emissivities
less than 0.1, 0.3 or 0.5.
[0022] The chamber 112 may include an exterior treatment 117a
applied on exterior surfaces of the chamber 112 and having a
relatively low emissivity or having a relatively high spectral
reflectivity to minimize the absorption of external radiation. As
examples, the exterior treatment 117a may include a low emissivity
coating, such as a coating including alumina (i.e., aluminum oxide
(Al.sub.2O.sub.3) or emissivity-reducing nanoparticles.
Alternatively, the exterior treatment 117a may include polishing
the exterior surfaces of the chamber 112 to lower the surface
emissivity of the chamber material and produce a relatively low
emissivity surface as described herein. In an exemplary embodiment,
the chamber 112 may be aluminum or copper with a highly polished
exterior surface, yielding in an emissivity less than 0.1. In at
least one embodiment, the exterior treatment 117a may be spectrally
reflective to reduce the absorption of external radiation by the
chamber 112. The chamber 112, with or without the exterior
treatment 117a, may reflect radiation in at least a portion of the
infrared wavelength range, as defined herein.
[0023] In certain embodiments, the chamber 112 may further include
an interior treatment 117b applied on interior surfaces of the
chamber 112. The interior treatment 117b may have a relatively low
emissivity including, for example, a low emissivity coating and/or
a polishing the interior surfaces, similar to treatments described
herein with respect to the exterior treatment 117a. Alternatively,
the interior treatment 117b may have a relatively high absorptivity
in the operational NIR range to reduce the reflectance of interior
surfaces of the chamber 112 in view of the detector 110 and to
reduce internal reflections that may fall incident upon the
detector 110. For example, the interior treatment 117b may have an
absorptivity greater than about 0.50, 0.70 or 0.90. The interior
treatment 117b may include black anodize, specific flat (i.e.,
matte) black paints or any suitable high absorptivity coating. In
certain embodiments, the interior treatment 117b may include a high
absorptivity foil applied to the chamber 112, such as those
manufactured by Acktar Ltd. and ACM Coatings GmbH, in which a high
absorptivity coating is applied to a foil or other substrate that
is subsequently applied to the chamber 112 to form the interior
treatment 117b. In certain embodiments, the interior treatment 117b
and the exterior treatment 117a may be the same treatment.
[0024] In at least one embodiment, the shield 100 may include a
shield window 114. In at least one embodiment, the shield window
114 is highly thermally conductive and, accordingly, is made of a
material having a relatively high thermal conductivity--for
instance, greater than 100 W/mK--and being highly transparent to
the operational NIR range of the spectrometer 102 and the detector
110. In such an embodiment, the shield window 114 may be composed
of glass (i.e., amorphous glass), glass-ceramic (i.e., at least
partially crystalline glass), diamond, crystalline quartz, silicon,
germanium, gallium nitride (GaN) crystals, AlN crystals, optical
metamaterial, transparent ceramic such as sapphire (i.e.,
single-crystal aluminum oxide), magnesium aluminate spinel
(MgAl.sub.2O.sub.4), aluminum oxynitride spinel
(Al.sub.23O.sub.27N.sub.5, often referred to as AlON), or other
suitably transparent and thermally conductive material, and
combinations of these materials.
[0025] Sapphire, crystalline quartz, silicon, germanium, GaN
crystals, AlN crystals and optical metamaterials generally have
higher thermal conductivity than many common glasses, and most
ceramics, and generally have excellent optical transmissivity to
infrared, which may attenuate generating thermal radiation from the
window 114 itself. Moreover, certain semiconductor materials, such
as those mentioned, enable optical transmission properties to be
modified via to doping, structural processing, growth conditions
and other means. Further, these semiconductor materials may
facilitate blocking visible fundamental radiation, which becomes
absorbed. In such an embodiment, the window 114 may have an inside
optical coating or surface modification that reflects at least
nearly all of the unwanted long wavelength thermal radiation.
[0026] In at least one embodiment, the shield window 114 may
include one or more coatings 116 formulated, structured and applied
to pass wavelengths within the desired operational NIR range and/or
to block other, undesired wavelengths. The coating 116 may further
be polarized to limit external radiation incident upon the interior
surfaces of the chamber 112 and the detector 110. The coating 116
may be any operably appropriate coating or filter technology such
as dielectric, anti-reflective, dichroic or rugate coatings and
filters. The coating 116 may be selected to enable a coating
operational wavelength range, including at least the desired
operational NIR range of the detector 110 and the spectrometer 102.
For example, the coating 116 may have a coating operational
wavelength range of about 0.4 to 2.5 microns or 1.0 to 1.31
microns. In certain embodiments, the coating 116 may further
include a short pass filter or bandpass filter coating to block
radiation at wavelengths above or outside the desired operational
wavelength range. As one example, the coating operational
wavelength range may by the range applicable to Raman spectroscopy,
and most unwanted thermal radiation will be at wavelengths above
the Raman range. The coating 116 enables the window 114 to block or
at least attenuate a significant amount of the unwanted radiation
from the surrounding hardware and scene, radiation that is
responsible for transmitting heat and hence background noise to the
detector 110. In at least one embodiment, the coating 116 may
include a layer that at least partial reflects, absorbs and/or
scatters radiation, or a combination thereof, in a specified
range.
[0027] In at least one embodiment according to the present
disclosure, the shield 100 may include a cooling device 120, as
shown in FIG. 1. The cooling device 120 enables the chamber 112 to
be cooled to an appropriate operational temperature for the
detector 110 (i.e., a desired detector temperature). In embodiments
including the shield window 114, the cooling device 120 enables
cooling of the shield window 114 and the chamber 112. In certain
embodiments, the cooling device 120 may be a solid-state cooler. In
such embodiments, the cooling device 120 may be a semiconductor
thermoelectric (TE) device (i.e., a Peltier device), such as a
thermoelectric cooler (TEC), structured to transfer heat from one
side of the device to the other across an n-p junction, upon
application of a voltage potential, depending on the direction of
the current. Certain such devices are designed to operate most
efficiently as either a cooler or a heater. Nonetheless, the
cooling device 120 may be a thermoelectric heat pump that can be
used as a temperature controller that either heats or cools.
[0028] In at least one embodiment, the cooling device 120 may be a
cyclic compression-expansion cooler. For example, the cooling
device 120 may be a closed-cycle, Stirling heat pump having a
regenerator to facilitate heat transfer from the shield 100. One
such device has been manufactured by Micro-Star International Co.,
Ltd of Taiwan. Alternatively, the cooling device 120 may be a
closed-cycle, Carnot heat pump using a reverse Carnot cycle to
facilitate heat transfer from the shield 100. In further
embodiments, the cooling device 120 may be a cryogenic cooler
(i.e., a cryocooler) using a liquefied gas in thermal communication
with the chamber 112. In such an embodiment, the liquefied gas may
include, but not be limited to, one or more of nitrogen, carbon
dioxide, methane, ethane, oxygen, hydrogen and the like.
[0029] The cooling device 120 may be configured to generate a
minimum heat pumping capacity to cool the shield 100 to a desired
shield temperature and to maintain the detector 110 at a desired
detector temperature. The cooling device 120 may have a heat
pumping capacity capable of a cooling range of around -20.degree.
C. to -120.degree. C. In certain applications, such as applications
for Raman spectroscopy, the cooling range may extend at least to
-60.degree. C. In at least one embodiment, the cooling device 120
may be a multi-stage cooling device having two or more stages and
capable of greater heat pumping capacity than a single-stage
cooler. For example, the cooling device 120 may have a first stage
capable of generating a first temperature delta across the first
stage to yield a first cooling temperature, and a second stage
capable of generating a second temperature delta across the second
stage to yield a second cooling temperature, where the second
cooling temperature is lower than the first cooling temperature.
Further, the cooling device 120 may have additional stages, each
capable of generating an additional temperature delta to yield ever
lower cooling temperatures, thereby increasing the total cooling
capacity of the cooling device 120.
[0030] The shield 100 may further include a thermal interface
material having relatively high thermal conductivity disposed
between the chamber 112 and the cooling device 120 to improve
thermal contact, reduce thermal resistance and facilitate heat
transfer therebetween. The thermal interface material may be a
thermal fluid, a thermal grease or paste, a resilient thermal
conductor, or solder applied in a molten state. In embodiments
incorporating thermal fluid, thermal grease or solder, the material
may be applied on at least the mating surfaces. In embodiments
incorporating a resilient thermal conductor, such as a metal or
metal oxide filled elastomer, the material may be placed between
the mating surfaces and held in place by assembly.
[0031] The chamber 112 and the cooling device 120 may include
feedthroughs 118 to transmit power to and/or signals from detector
110 and to enable control of the cooling device 120. Such
feedthroughs 118 may be routed through a bottom portion of the
dewar 104, as shown in FIG. 1.
[0032] FIG. 2 illustrates a radiation shield 200 according to a
further embodiment of the present disclosure. As shown in FIG. 2,
the shield 200 may include a multi-stage cooling device 220 having
a first stage 221 and a second stage 222. The shield 200 may
include a chamber 212 having a bottom opening 213 in a wall
adjacent the cooling device 220. The opening 213 may be configured
to enable at least a portion of the cooling device 220, for
example, the second stage 222, to protrude at least partially
through the chamber 212. The opening 213 enables contact and direct
thermal communication between the chamber 212 and a desired stage
of the multi-stage cooling device 220. In FIG. 2, the chamber 212
is in direct thermal communication with the first stage 221. In
such an embodiment, the cooling device 220 may cool the chamber 212
to an intermediate temperature below the ambient or surroundings
temperature, driven substantially by the first stage 221, and the
cooling device 220 may further cool the detector 110 to a target
temperature that is lower than the intermediate temperature, driven
substantially by the second stage 222. In certain embodiments, the
first stage 221 may be an intermediate stage and the second stage
222 may be a final stage of a multi-stage TE stack having more than
two stages.
[0033] The chamber 212 with the opening 213 provides an efficient
and effective thermal interface to the first stage 221 of the
multi-stage cooling device 220, which enables the shield 200 to
operate at a desired intermediate temperature that is in between
the external, ambient temperature and that of the desired operating
temperature of the detector 110. In doing so, the thermal load on
the second stage 222 is reduced, enabling more efficient operation
of the cooling device 220 and/or lower operating temperature of the
detector 110. With the multi-stage cooling device 220, there may be
a point of diminishing returns at some intermediate shield
temperature, below which thermal radiation from shield 200 is no
longer significant with respect to the inherent dark current of the
colder detector 110. In at least one embodiment, the cooling device
220 may be a multi-stage thermoelectric cooler (i.e., a TEC stack)
having two or more stages and capable of greater heat pumping
capacity than a single-stage thermoelectric cooler. Exemplary TECs
are manufactured by Marlow Industries, Inc. and TE Technology,
Inc., among others.
[0034] Referring to FIG. 1, in certain embodiments of the present
disclosure, the dewar window 106, shield window 116, and detector
110 may be in relatively close proximity. In such embodiments,
improvements in attenuating unwanted incident radiation, which are
facilitated by the separate shield window 114 with the coating 116,
may be limited because of the larger solid angle over which the
coating 116 (e.g., a dielectric filter coating) on the shield
window 114 must operate to effectively prevent external radiation
from reaching the detector 110. In such embodiments, the aperture
113 may be left open (i.e., the shield window 114 may be omitted),
leaving no optical material (either a shield window or a shield
window coating) between the detector 110 and the dewar window
106.
[0035] FIG. 3 illustrates a dewar 304 surrounding the shield 200
according to a further embodiment of the present disclosure. As
shown in FIG. 3, the shield 200 need not include a shield window.
In such embodiments, the dewar 304 may include a dewar window 306
having a coating 316. The dewar window 306 with the coating 316
attenuates unwanted incident radiation that may be difficult to
filter where the dewar window 306, chamber 212, and detector 110
are in relatively close proximity.
[0036] The coating 316 may be the same or substantially the same as
the coating 116, depending on the composition of the dewar window
306. Accordingly, the coating 316 may have a coating operational
wavelength range of about 0.4 to 2.5 microns. In certain
embodiments, the coating 316 may further include a short pass
filter or bandpass filter coating to block radiation at wavelengths
above or outside the desired operational wavelength range. As one
example, the coating operational wavelength range may by the range
applicable to Raman spectroscopy, and most unwanted thermal
radiation will be at wavelengths above the Raman range. The coating
316 enables the dewar window 306 to block or at least attenuate a
significant amount of the unwanted radiation from the surrounding
hardware and scene, radiation that is responsible for transmitting
heat and hence background noise to the detector 110.
[0037] In a further embodiment according to the present disclosure,
a radiation shield 400 is shown in FIG. 4. In FIG. 4, the shield
400 is shown disposed within the dewar 104, and the spectrometer
102 is not shown. The shield 400 may include a chamber 412 having
an opening 413. The shield 400 may further include a multi-stage
cooling device 420 including a first stage 421 and a second stage
422, the second stage 422 having an opening or void 423 configured
to enable to place at least a portion of the detector 110 to
thermal communication with the first stage 421 but in isolation
from the second stage 422 and the chamber 412, which may contact
the second stage 422. In such an embodiment, the cooling device 420
may be configured such that the detector 110 lies on a different
plane than the chamber 412, as shown in FIG. 4. The opening 413
enables contact and direct thermal communication between the
chamber 412 and a cooler stage of the multi-stage cooling device
420, thereby enabling the chamber 421 to be cooled to a lower
temperature than the detector 110.
[0038] As shown in FIG. 4, the chamber 412 may be in direct thermal
communication with the second stage 422, which may be cooler than
the first stage 421. In such an embodiment, the cooling device 420
may cool the detector 110 to an intermediate temperature below the
ambient or surroundings temperature, driven substantially by the
first stage 421, and the cooling device 420 may further cool the
chamber 412 to a target temperature that is lower than the
intermediate temperature, driven substantially by the second stage
422. In certain embodiments, the first stage 421 may be an
intermediate stage and the second stage 422 may be a final stage of
a multi-stage cooler having more than two stages.
[0039] The cooling device 420 with the opening or void 423 and
chamber 412 with the opening 413 provides an efficient and
effective thermal interface to the second stage 422 of the
multi-stage cooling device 420, which enables the shield 400 to
operate at a desired temperature that is lower than the desired
operating temperature of the detector 110. In doing so, potentially
interfering radiation emitted by the chamber 412 is reduced,
improving the signal to noise ratio of the detector 110. With the
multi-stage cooling device 420, there may be a point of diminishing
returns at some shield temperature, below which thermal radiation
from shield 400 is no longer significant with respect to the
inherent dark current of the detector 110.
[0040] While various embodiments of a radiation shield for a NIR
detector have been described in considerable detail herein, the
embodiments are merely offered by way of non-limiting examples of
the disclosure described herein. It will therefore be understood
that various changes and modifications may be made, and equivalents
may be substituted for elements and steps thereof, without
departing from the scope of the disclosure. Indeed, this disclosure
is not intended to be exhaustive or to limit the scope of the
subject matter disclosed.
* * * * *